These studies will investigate the effects of maternal dietary salt excess, on BP development in offspring of genetically hypertensive rats, postulating that: the development and severity of hypertension in a susceptible individual could be modified by salt excess acting during pre-natal and early post-natal life. A hypertension susceptible mother with an excessive salt intake transmits to the offspring via milk, a factor(s) which in interaction with renal immaturity aggrevates offspring hypertension. After weaning, different environments associated with the offspring's new stage of life modulate the final course of BP through maturity. To test this hypothesis we will use a cross-suckling design and multivariate analysis. The spontaneously hypertensive rat (SHR) and the control Wistar-Kyoto rat (WKY) will be used; the environmental factor will be NaC1 in the diet of mother, nurse and weanling. The diet salt content (low 0.3% and high 4%) will be manipulated at three spans: pregnancy, lactation, and post-weanling stage. SHR and WKY dams will be pair-matched for BP and randomly assigned to 0.3% or 4% salt diets for one week (4 groups) prior to mating and maintained on their assigned diets until delivery. Then one "environmental" and one "genetic" manipulation will be done. Each mother will be a nurse and her diet will be randomly assigned to either low or high salt (8 groups). Half the male pups of each strain will then be cross-suckled (16 groups). All pups will be weaned at 19 days, and the pup's diet randomized to high or low salt (32 groups). Maternal endpoints will be: body weight, BP, heart rate, food and water intake (days 7, 15, and 20 post-mating, and 7 and 18 post-partum); circadian milk Na, K, water, fat, protein, and lactose content (days 7 and 19 post-partum). Offsprings end point will be: milk "intake" at 7 days by tritiaded water administration to the mother; body weight, BP, heart rate, plasma volume, carcass Na, K, water content and renal studies (kidney weight, DNA/protein ratio, microscopy and glomerular number) at 0 and 7 days; plasma volume, BP and renal studies at 19 days and BP and renal studies on 140 days. Postweanling pups will have BP measurements every 2-4 weeks for one year. Micropuncture will be used to measure BP, heart rate and plasma volume in sucklings; established methods will be used for glomerular count, kidney DNA/protein ratio, and renal morphology. This proposal will dissect the role of maternal environment and genetics in the development of body fluids, kidney and hypertension, which will provide a rationale for preventative measures in the hypertension prone individual.